Alternator



BEST AVASLABLE COP;

-' F. W. MERRILL Aug. 24, 1926.

ALTERNATOR Filed Jan. 13, 1925 Inventor: Frank W. M er-rill,

H is Attorney Patented Aug. 24, 1926.

BEST AVAILABLE CUP.

PAT

ENT OFFICE.

FRANK V7. MERRILL, OF FORT WAYNE, INDIANA, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

ALTERNATOR.

Application filed January 13, 1925.

My invention relates to alternators, and particularly to a new and novel alternator which will directly produce an interrupted current of relatively high frequency with a relatively low frequency of interruption.

It has been the practice in the art of telephony to signal by means of an interrupted current, having a relatively high frequency of say from 137 to 1000 cycle per second and interrupting this high frequency current at a frequency of to cycle per second, thus giving alternate silent and signal periods. The interruption of the current at this low frequency has been accomplished heretofore by means of a mechanical interrupter. Such interrupters have been found dilficult to build and maintain.

In accordance with my invention, I generate such an interrupted current directly and thus eliminate allmechanical interrupters. To. this end, I construct an alternator with two relatively rotatable. members, one of which has a poleand an alternating current winding surrounding the pole, the other of which h'asfteeth and spaces therebetween extending over onlya portion of its periphery. itli'such a construction, the relative rotation pf themembers produces an alternating currentivoltage in the alternating current during a portion of each, revolution of one member with refer ence toffthe' other andlno voltage during another portion of each revolution.

Other features of novelty which characterize my invention are 'poin'ted out with particularity in theclaims annexed to and forming a partof this specification. Fora better understanding of my invention, reference may be had to the following description taken in connection with the accompanying-drawing, in which Fig. 1 is a view of an alternator'embodyingmy invention; Fig. 2 is a view of an alternator embodying a modification, and Fig. 3-,is a diagram of the voltage curve of iny alternator.

Referring to 'Fig. 11 of the drawing, the alternator therein shown is of the inductor type and has two relatively rotatable mem here 1 and 2. The stationary member or stator 1 is shown as having four narrow poles 3 and 4', each of which is surrounded Serial No. 2.213.

by a winding 5 or 6. The rotatable member or rotor 2 has teeth 7 with spaces 8 therebetween, these teeth and spaces being equally spaced but extending over only a portion of the periphery of the rotor 2. The other portion of the rotatable member is smooth and cylindrical in form. The teeth '7 are substantially equal in width to the width of; the poles 3 and 4t. A direct current field winding 9 is mounted on the stationary member and is' supplied with current from lines 10'. The field winding 9 comprises two coils, each surrounding two of the poles on the stationary member. This field winding produces a magnetic flux which, flows through the poles 3'and 4 and the teeth 7'. In the arrangement shown'in this figure, the teeth 7'extend over only one-half of the periphery of the rotatable member, sothat thedistance betweenthe poles 3 on one side ofthe stationary, member and-the poles 4 onthe other side. is substantially equal to thesinooth portion of the rotatable member. {Each of the wi'ndings 5 onthe poles 3 on the' left hand side of Fig. 1 are shown as connected ma independentjcircuit. Considernowf one" of these windings with the rotatable member 'in the-position shown in Fig. 1: Flux'flows from the stationary memher 1 through a pole 3 then across the air gap through a tooth? on the rotatable'member, through the'j rotatableunemb'er to the smooth portion thereof, across 'the'air gap through a pole t on the'righteharid'si'de of 1 and back to'the stationary member 1 W'hen the rotatable member haslm'oved" so that'sp'ace' 8 comes opposite'the pole 30171 the left-hand side, very little ffiun flows therethrough. It will, therefore, beseen that as the'toothed portion of the rotatable member passes under thispole. 3, the flux throughsuch pole will vary from. a maximum to a minimum and then'will rise again to a maximum, generating ajoltage, in the winding 5 surrounding thijspole, of 'a relatively high frequency during a half revolution. The frequency is equal to'twice the number of teeth 7 times the numberof revo lutions of the rotatable member. Assume that the.rotatableinember is revolving at 1175 R. P. M., that is, l9'.6 R. P. S, and that there are 25 teeth thereon (51 teeth if they extended completely around the pe riphcry) the frequency of the current generated while the toothed portion the rotat able nembebis passing the pole 3 would be 19.6 X 51, "that is 1000'cycles per second. When the smooth portion of the rotatable member: is passing this pole 3; there will be no variation in the that; passing therethrough and consequently novoltage will he generated in the winding 5, thus interrupting the high frequency current during onehalf of each revolution" of th'e"'rotatable member. lVith a speed of 1175 R. P. ll-f1". the interruptions will be at a'rate b f '19. cycle per secondl' If'thewindings'abouttwo adjacent poles are connected in series as shown oh the right of the roltage produced 'will be twice that at sing e winding as on the left of Fig. 1, there. will 'be produced a shaded interruption of" tone extending'ove'r about tliree'rptor teeth at each end or a half revolution' The ijolta e wa g'eproduced by such a ion'isils howiiin Eigjii. This conhit h advan g a the altel? nating'current' 'wa've'bf'voltage will have fewer" harmonies than the wave produced in a sing e y inding. connected to a circuit, as shown On the'leftof Fig; l. If now the windin'ion a pole 3 (or'the two windings u i 0 on ad acent poles 3 on the left side of the maohine'is connec ed to one circuit and the wi iding 6 on a pole 4 (or the two windna dia nt "P the r gh id of the machine is" connected to another cir} cuit, each circuit will have supplied thereto an interrupted current of relatively high frequency with a relati ely low 'frequen cjr of interruption, the high frequency current being supplied in one circuit while the cur} rent in the ther circuit is being interrupted,

and vice versa.

' Vhile the toothed portion of the rotatable member is passing undera pole on one side of the stationary member, it is important that there be no appreciable variation in'the fiun fed to the poles on the other side of the'stationary meinber by the smooth portion of the rotatable member. Any variation in the flux fed to the poles by the smooth portion of the rotatable member will produce a 'voltage in the windings surround; ing these poles and cause noise in a supposedly quiet circuit. The poles opposite the toothed portions of the rotatable member should therefore as a whole, supply constant flux to' the rotatable member, that, is, the flux which is rapidly varying in, each pole should add up to'a constant value. This result is accomplished by making the pitch of the poles equal to a fractional pitch of the rotor. teeth, such as 1 2 etc. The pit-ch'sho'wn in Fig. 1 is 2 This means that when onerotor tooth con'ies'e'xactly in BEST AVAILABLE COP line with any one. stator pole and draws maximum flux through the stator pole, the adjacent stator pole is opposite a space between rotor teeth and in the position of minimum flux. i

If the air gap under the poles on the righthand side of the machine is different from at n e thos n h e -ha d Side, iiixiinum minimum flux passing through the stator poles on the two sides is different when the toothed portion of the rotatable member passes thesestator poles. 'lhis ivill result in 'a different voltage being generated in the circuits of the windings stra-m'mdingahe poles saute msiues'. 'In ordert'o insure tha t'the air gap is uniform under t-he pol'es on both sides'fl mount the stationary member 1 in aframe"ll'"with si iicient'clearance between them to permit the frame without distorting 'or springing the lan'iinations of the stationary member, and proi'i'cle 'set screws 12 'nga ing' tlie frame and the statidnarji member. ypropcrlymori ng these set s .crews','the air gapand the stator poles on 'bothsides can be made exit-n equalf If a large number of poles are provided on the stationary mcmber and all of such poles are not p'rovi'de'dhtith windings, u); variations would occur in'the poles proi'i zl ed with windings, due to the. passage. ofthe low reluctance smooth portion of the rota} tableinenibei under the idle oles of the stationary member, which won not place with the arrangement of Fig. l.

if, however, it is desired to bare large a ni of i s epse e e r i 'e' inmii requiring a large number 6f poles on the stationary member, it is desirable to reduce the diameter ofthe smooth portion of the rotata blc'member below that of the outside diameter of the toothed portion, This reduction in diameter should Sttli ltl'iQllt to give the sanic' reluctance as the average reinctance of the toothed portion, I i this wa the total, flux would be substantially. constant. six circuits are desired, the best results would be obtained by winding three cireuits on each side. one circuit on each of three poles, or one circuit on each adjacent pair of sixpoles on each side. Twelve circuits-one on each of twelve poles-could also be provided, i

In the modification shown in lfig, 2, the rotatable member isdivided into four equal parts, two opposite parts being proyidegl with teeth I 'andspace's 8 thercgbetween, and the other two opposite parts" being smooth. The direct current field windingSQsuppIEed with current from lines 1Q is shown as'proriding a bipolar excitation. The two of adjacent stator pol'es'4' on the'rightlmnd side of this figure have 'indings'6"coiinested in separate circuits, and these windings will have generated therein interrupted high frequency currents, the interruptions occurring twice for each revolution, so that if the rotatable member 2 is revolved at 1175 R. P. M.-l9.6 R. P. S.-the interruptions will be at a frequency of 39.2 cycles per second.

The stator poles 3 at the upper part of the left-hand side of Fig. 2 are wound with windings 5 having a different number of turns than the windings 13 on the stator poles 3 at the lower part of the left-hand side, the windings of all of these poles be ing connected in series. The windings on one set of these poles will have no voltage generated therein when the smooth portion of the rotatable member is passing under them, while the other set of these poles will have a high frequency voltage generated therein, and since the two sets of windings are in series, the voltage supplied to the circuit to which these windings are connected will vary in amount proportional to the number of turns in the respective windings. If these poles were all wound with the same number of turns and connected in series, the voltage supplied the circuit would be an uninterrupted high frequency one, as one set of poles will stop generating at the same time that the other set starts generating, and vice versa. The stator poles in Fig. 2 are narrow and substantially equal in width to the width of the rotor teeth and the pitch of these poles is the shortest possible being equal to one-half of the rotor tooth pitch. This gives the sharpest possible interruption without sacrificing the wave shape or the uniform total flux through the field windings.

Other modifications of my invention will be apparent to those skilled in the art, and I desire it to be understood that I aim in the appended claims to cover all such modifications which do not depart from the spirit and scope of my invention.

\Vhat I claim as new and desire to secure by Letters Patent of the United States, is

1. An alternator comprising two relatively rotatable members, one of the members having an annular face provided with teeth on afractional part only thereof, the other of the members having poles arranged adjacent said one member and spaced apart such that one pole is opposite atooth when another pole is opposite a space between two teeth, windings on said poles and means for producing flux through saio poles and teeth, whereby relative movement of said members causes alternating current voltages to be induced in the windings at successive intervals.

2. An alternator comprising a rotor having its periphery divided into toothed and substantially smooth portions, a stator having a pair of poles adjacent said face and BEST AVAILABLE cos a spaced apart so that when one pole is opposite a tooth of the rotor the other pole is opposite a space between two teeth, winding on said poles and a field winding for producing a fiux between the poles of the stator and the rotor.

3. An alternator comprising a rotor having its periphery divided into toothed and substantially smooth portions, a stator having a pair of poles adjacent said face and spaced apart so that when one pole is opposite a tooth of the rotor the other pole is opposite a space between two teeth, a second pair of similar poles displaced from the first pair of poles substantially the length of one of said portions, windings on said poles and a field winding for producing a fiux between the poles of the stator and the rotor.

t. An alternator comprising a rotor having its periphery provided with teeth in (ertain portions and substantially smooth in other portions, a stator surrounding the rotor, a pair of poles on the stator spaced such that when one pole is opposite a tooth of the rotor the other pole is opposite a space between teeth, a second similar pair of poles on the stator circumferentially dis placed from the first pair of poles a distance corresponding to the length of a smooth portion of the rotor, windings on said poles, and a field winding for producing flux through the rotor, the stator and the poles.

In an alternator, a frame member, a stationary member mounted therein hav ng a pole and a winding surrounding said pole, a rotatable member having teeth with spaces therebetween on its periphery, said teeth and spaces extending over a portion only of its periphery, means engaging said frame and said stationary member for adjusting the air gap between said pole on the stationary member and said rotatable member, and means for producing flux through said pole on the stationary member and the teeth on the rotatable menber. the rotation of said rotatable memberpio ducing an alternating current voltage in said winding during a'portion of each revolution of said rotatable member and no voltage in said winding during another portion of each revolution of said rotatable member.

(3. In an alternator, a frame member, a stationary member mounted therein having pole. spaced apart and windings surround in said poles, a rotatable member having teeth with spaces therebetween on its pcriphery, said last mentioned teeth and spaces extending over aportion only of its periphery, the remainder of said periphery being smooth and cylindrical in form, the distance between the poles on the stationary member being substantially equal to the smooth portion of the periphery of the rotionary member-and said rotatablemember 5 and meansfor;praducingfiuxthrough said poles and teeth, the rotation of saidrotatablememberproducingan aIt-ernatingcur- 358T AVNLABLE COPE rentvoltage in one of saidwwinc fings and no voltage in the other of said Winding-s during, a portion of each revolution of said" 30 rotatable member;

In Witness whereof, I have:h'ereuntO-set my handthis 9th day 0fvJanu ary1925 A, FRANK WV. MERRILL." 

